Garnets () are a group of silicate minerals that have been used since the

Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second pri ...

as gemstones and

abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...

s. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different species are pyrope,

almandine Almandine (), also known as almandite, is a species of mineral belonging to the garnet group. The name is a corruption of alabandicus, which is the name applied by Pliny the Elder to a stone found or worked at Alabanda, a town in Caria in A ...

spessartine Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. Gemological Institute of America, ''GIA Gem Reference Guide'' 1995, This mineral is sometimes mistakenly referred to as ''spessartite''. Spessartine's name i ...

, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and

andradite Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12. Andradite includes three varieties: * ''Melanite'': Black in color, referred to as "titanian andradite".solid solution series: pyrope-almandine-spessartine (pyralspite), with the composition range ; and uvarovite-grossular-andradite (ugrandite), with the composition range .

Etymology

The word ''garnet'' comes from the 14th-century

Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English ...

word ''gernet'', meaning 'dark red'. It is borrowed from Old French ''grenate'' from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''granatus,'' from ''granum'' ('grain, seed'). This is possibly a reference to ''mela granatum'' or even ''pomum granatum'' (' pomegranate', ''Punica granatum''), a plant whose fruits contain abundant and vivid red seed covers ( arils), which are similar in shape, size, and color to some garnet crystals.

Physical properties

Properties

Garnet species are found in every colour, with reddish shades most common. Blue garnets are the rarest and were first reported in the 1990s. Garnet

Garnet species' light transmission properties can range from the gemstone-quality transparent specimens to the opaque varieties used for industrial purposes as abrasives. The mineral's luster is categorized as vitreous (glass-like) or resinous (amber-like).

Crystal structure

Garnets are nesosilicates having the general formula ''X''₃''Y''₂()₃. The ''X'' site is usually occupied by divalent cations ( Ca, Mg, Fe, Mn)²⁺ and the ''Y'' site by trivalent cations ( Al, Fe, Cr)³⁺ in an octahedral/ tetrahedral framework with iO₄sup>4− occupying the tetrahedra. Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the

trapezohedron In geometry, an trapezohedron, -trapezohedron, -antidipyramid, -antibipyramid, or -deltohedron is the dual polyhedron of an antiprism. The faces of an are congruent and symmetrically staggered; they are called ''twisted kites''. With a high ...

habit as well as the hexoctahedral habit. They crystallize in the

cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...

system, having three axes that are all of equal length and perpendicular to each other, but are never actually cubic because, despite being isometric, the and families of planes are depleted. Garnets do not have any cleavage planes, so when they fracture under stress, sharp, irregular (

conchoidal Conchoidal fracture describes the way that brittle materials break or fracture when they do not follow any natural planes of separation. Mindat.org defines conchoidal fracture as follows: "a fracture with smooth, curved surfaces, typically slig ...

) pieces are formed. File:Pyrope cp.jpg, Crystal structure of pyrope garnet. White spheres are oxygen; black, silicon; blue, aluminium; and red, magnesium. File:Pyrope crystal structure.jpg, Same view, with ion sizes reduced to better show all ions File:Pyrope si.jpg, Silicon ion size exaggerated to emphasize silica tetrahedra

Hardness

Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this mineral group shows a range of hardness on the Mohs scale of about 6.0 to 7.5. The harder species like

are often used for abrasive purposes.

Magnetics used in garnet series identification

For gem identification purposes, a pick-up response to a strong

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separates garnet from all other natural transparent gemstones commonly used in the jewelry trade. Magnetic susceptibility measurements in conjunction with refractive index can be used to distinguish garnet species and varieties, and determine the composition of garnets in terms of percentages of end-member species within an individual gem.

Garnet group end member species

Pyralspite garnets – aluminium in ''Y'' site

Almandine Almandine (), also known as almandite, is a species of mineral belonging to the garnet group. The name is a corruption of alabandicus, which is the name applied by Pliny the Elder to a stone found or worked at Alabanda, a town in Caria in A ...

: Fe₃Al₂(SiO₄)₃ * Pyrope: Mg₃Al₂(SiO₄)₃ *

Spessartine Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. Gemological Institute of America, ''GIA Gem Reference Guide'' 1995, This mineral is sometimes mistakenly referred to as ''spessartite''. Spessartine's name i ...

: Mn₃Al₂(SiO₄)₃
Grossular-ww51a

Almandine

Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle (though originally almost any red gemstone was known by this name). The term "carbuncle" is derived from the

meaning "live coal" or burning charcoal. The name ''Almandine'' is a corruption of Alabanda, a region in

Asia Minor Anatolia, tr, Anadolu Yarımadası), and the Anatolian plateau, also known as Asia Minor, is a large peninsula in Western Asia and the westernmost protrusion of the Asian continent. It constitutes the major part of modern-day Turkey. The ...

where these stones were cut in ancient times. Chemically, almandine is an iron-aluminium garnet with the formula Fe₃Al₂(SiO₄)₃; the deep red transparent stones are often called precious garnet and are used as gemstones (being the most common of the gem garnets). Almandine occurs in

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, cau ...

s like

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

schists, associated with minerals such as staurolite, kyanite, andalusite, and others. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle.

Pyrope

Pyrope (from the Greek ''pyrōpós'' meaning "firelike") is red in color and chemically an aluminium silicate with the formula Mg₃Al₂(SiO₄)₃, though the magnesium can be replaced in part by calcium and ferrous iron. The color of pyrope varies from deep red to black. Pyrope and spessartine gemstones have been recovered from the Sloan diamondiferous kimberlites in

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

, from the Bishop Conglomerate and in a Tertiary age

lamprophyre Lamprophyres () are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica- undersaturated mafic or ultramafic rocks with high magne ...

at Cedar Mountain in

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the sou ...

. A variety of pyrope from Macon County,

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia a ...

is a violet-red shade and has been called ''rhodolite'', Greek for "rose". In chemical composition it may be considered as essentially an isomorphous mixture of pyrope and almandine, in the proportion of two parts pyrope to one part almandine. Pyrope has tradenames some of which are misnomers; ''Cape ruby'', ''Arizona ruby'', ''California ruby'', ''Rocky Mountain ruby'', and ''Bohemian ruby'' from the

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. Th ...

. Pyrope is an indicator mineral for high-pressure rocks.

Mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

-derived rocks ( peridotites and eclogites) commonly contain a pyrope variety.

Spessartine

Spessartine or spessartite is manganese aluminium garnet, Mn₃Al₂(SiO₄)₃. Its name is derived from

Spessart Spessart is a '' Mittelgebirge'', a range of low wooded mountains, in the States of Bavaria and Hesse in Germany. It is bordered by the Vogelsberg, Rhön and Odenwald. The highest elevation is the Geiersberg at 586 metres above sea level. Et ...

Bavaria Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total l ...

. It occurs most often in skarns,

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies und ...

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic co ...

and allied rock types, and in certain low grade metamorphic phyllites. Spessartine of an orange-yellow is found in Madagascar. Violet-red spessartines are found in rhyolites in

Pyrope–spessartine (blue garnet or color-change garnet)

Blue pyrope–spessartine garnets were discovered in the late 1990s in Bekily,

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

. This type has also been found in parts of the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eigh ...

Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

, and

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...

. It changes color from blue-green to purple depending on the

color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...

of viewing light, as a result of the relatively high amounts of vanadium (about 1 wt.% V₂O₃). Other varieties of color-changing garnets exist. In daylight, their color ranges from shades of green, beige, brown, gray, and blue, but in incandescent light, they appear a reddish or purplish/pink color. This is the rarest type of garnet. Because of its color-changing quality, this kind of garnet resembles alexandrite.

Ugrandite group – calcium in ''X'' site

Andradite Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12. Andradite includes three varieties: * ''Melanite'': Black in color, referred to as "titanian andradite".Grossular: Ca₃Al₂(SiO₄)₃ * Uvarovite: Ca₃Cr₂(SiO₄)₃

Andradite

Andradite is a calcium-iron garnet, Ca₃Fe₂(SiO₄)₃, is of variable composition and may be red, yellow, brown, green or black. The recognized varieties are demantoid (green), melanite (black), and topazolite (yellow or green). Andradite is found in skarns and in deep-seated

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or l ...

s like syenite as well as serpentines and greenschists. Demantoid is one of the most prized of garnet varieties.

Grossular

Grossular is a calcium-aluminium garnet with the formula Ca₃Al₂(SiO₄)₃, though the calcium may in part be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the botanical name for the

gooseberry Gooseberry ( or (American and northern British) or (southern British)) is a common name for many species of ''Ribes'' (which also includes Ribes, currants), as well as a large number of plants of similar appearance. The berries of those in th ...

, ''grossularia'', in reference to the green garnet of this composition that is found in

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part o ...

. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow. Because of its inferior hardness to

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

, which the yellow crystals resemble, they have also been called ''hessonite'' from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

meaning inferior. Grossular is found in skarns, contact metamorphosed

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

s with vesuvianite,

diopside Diopside is a monoclinic pyroxene mineral with composition . It forms complete solid solution series with hedenbergite () and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dul ...

, wollastonite and wernerite. Grossular garnet from

Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...

and

has been called tsavorite. Tsavorite was first described in the 1960s in the Tsavo area of Kenya, from which the gem takes its name.

Uvarovite

Uvarovite is a calcium chromium garnet with the formula Ca₃Cr₂(SiO₄)₃. This is a rather rare garnet, bright green in color, usually found as small crystals associated with chromite in peridotite, serpentinite, and kimberlites. It is found in crystalline

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorpho ...

s and schists in the

Ural mountains The Ural Mountains ( ; rus, Ура́льские го́ры, r=Uralskiye gory, p=ʊˈralʲskʲɪjə ˈɡorɨ; ba, Урал тауҙары) or simply the Urals, are a mountain range that runs approximately from north to south through western ...

of Russia and Outokumpu, Finland. Uvarovite is named for Count Uvaro, a Russian imperial statesman.

Less common species

*Calcium in ''X'' site ** Goldmanite: **Kimzeyite: **Morimotoite: **Schorlomite: *Hydroxide bearing – calcium in ''X'' site **

Hydrogrossular Hydrogrossular is a calcium aluminium garnet series (formula: Ca3Al2(SiO4)3−''x''(OH)4''x'', with hydroxide (OH) partially replacing silica (SiO4)). The endmembers of the hydrogarnet family (grossular, hibschite, and katoite) depend on the deg ...

: ***Hibschite: (where x is between 0.2 and 1.5) ***Katoite: (where x is greater than 1.5) *Magnesium or manganese in ''X'' site ** Knorringite: ** Majorite: ** Calderite:

Knorringite

Knorringite is a magnesium-chromium garnet species with the formula Mg₃Cr₂(SiO₄)₃. Pure endmember knorringite never occurs in nature. Pyrope rich in the knorringite component is only formed under high pressure and is often found in kimberlites. It is used as an indicator mineral in the search for

diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...

Garnet structural group

*Formula: X₃Z₂(TO₄)₃ (X = Ca, Fe, etc., Z = Al, Cr, etc., T = Si, As, V, Fe, Al) **All are cubic or strongly pseudocubic. *IMA/CNMNC – Nickel-Strunz – Mineral subclass: 09.A Nesosilicate ** Nickel-Strunz classification: 09.AD.25 *References:

Mindat.org Mindat.org is a non-commercial online database, claiming to be the largest mineral database and mineralogy, mineralogical reference website on the Internet. It is used by professional mineralogists, geologists, and amateur mineral collecting, mi ...

; mineral name, chemical formula and space group (American Mineralogist Crystal Structure Database) of the IMA Database of Mineral Properties/ RRUFF Project, Univ. of Arizona, was preferred most of the time. Minor components in formulae have been left out to highlight the dominant chemical endmember that defines each species.

Synthetic garnets

Also known as rare-earth garnets. The crystallographic structure of garnets has been expanded from the prototype to include chemicals with the general formula ''A''₃''B''₂(''C''O₄)₃. Besides silicon, a large number of elements have been put on the ''C'' site, including

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbo ...

gallium Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group ( alum ...

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It h ...

, vanadium and

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

. Yttrium aluminium garnet (YAG), Y₃Al₂(AlO₄)₃, is used for

synthetic Synthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic o ...

gemstones. Due to its fairly high refractive index, YAG was used as a diamond simulant in the 1970s until the methods of producing the more advanced simulant cubic zirconia in commercial quantities were developed. When doped with neodymium (Nd³⁺), YAG may be used as the lasing medium in Nd:YAG lasers. When doped with erbium, it can be used as the lasing medium in Er:YAG lasers. When doped with gadolinium, it can be used as the lasing medium in Gd:YAG lasers. These doped YAG lasers are used in medical procedures including laser skin resurfacing, dentistry, and ophthalmology. Interesting magnetic properties arise when the appropriate elements are used. In yttrium iron garnet (YIG), Y₃Fe₂(FeO₄)₃, the five iron(III) ions occupy two octahedral and three tetrahedral sites, with the yttrium(III) ions coordinated by eight oxygen ions in an irregular cube. The iron ions in the two coordination sites exhibit different spins, resulting in

magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles ...

behavior. YIG is a ferrimagnetic material having a

Curie temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cu ...

of 550 K. Yttrium iron garnet can be made into YIG spheres, which serve as magnetically tunable

filters Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component th ...

and resonators for

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...

frequencies.

Lutetium aluminium garnet Lutetium aluminum garnet (commonly abbreviated LuAG, molecular formula Lu3Al5O12) is an inorganic compound with a unique crystal structure primarily known for its use in high-efficiency laser devices. LuAG is also useful in the synthesis of transpa ...

(LuAG), , is an inorganic compound with a unique crystal structure primarily known for its use in high-efficiency laser devices. LuAG is also useful in the synthesis of transparent ceramics. LuAG is particularly favored over other crystals for its high density and thermal conductivity; it has a relatively small lattice constant in comparison to the other

rare-earth The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides ( yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous sil ...

garnets, which results in a higher density producing a crystal field with narrower linewidths and greater energy level splitting in absorption and emission. Terbium gallium garnet (TGG), , is a Faraday rotator material with excellent transparency properties and is very resistant to laser damage. TGG can be used in optical isolators for laser systems, in optical circulators for fiber optic systems, in optical modulators, and in current and

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

sensors. Another example is gadolinium gallium garnet (GGG), which is synthesized for use as a substrate for liquid-phase epitaxy of magnetic garnet films for

bubble memory Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as ''bubbles'' or ''domains'', each storing one bit of data. The material is arranged to form a series o ...

and magneto-optical applications.

Geological importance

The mineral garnet is commonly found in metamorphic and to a lesser extent, igneous rocks. Most natural garnets are compositionally zoned and contain inclusions. Its crystal lattice structure is stable at high pressures and temperatures and is thus found in green-schist facies metamorphic rocks including

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

, hornblende schist, and mica schist. The composition that is stable at the pressure and temperature conditions of Earth's mantle is pyrope, which is often found in peridotites and kimberlites, as well as the serpentines that form from them. Garnets are unique in that they can record the pressures and temperatures of peak metamorphism and are used as geobarometers and geothermometers in the study of geothermobarometry which determines "P-T Paths", Pressure-Temperature Paths. Garnets are used as an index mineral in the delineation of isograds in metamorphic rocks. Compositional zoning and inclusions can mark the change from growth of the crystals at low temperatures to higher temperatures. Garnets that are not compositionally zoned more than likely experienced ultra high temperatures (above 700 °C) that led to diffusion of major elements within the crystal lattice, effectively homogenizing the crystal or they were never zoned. Garnets can also form metamorphic textures that can help interpret structural histories. In addition to being used to devolve conditions of metamorphism, garnets can be used to date certain geologic events. Garnet has been developed as a U-Pb geochronometer, to date the age of crystallization as well as a thermochronometer in the (U-Th)/He system to date timing of cooling below a closure temperature. Garnets can be chemically altered and most often alter to serpentine, talc, and chlorite.

Uses

Flickr - portableantiquities - Hilt Fitting

Gemstones

Red garnets were the most commonly used gemstones in the Late Antique Roman world, and the Migration Period art of the "

barbarian A barbarian (or savage) is someone who is perceived to be either uncivilized or primitive. The designation is usually applied as a generalization based on a popular stereotype; barbarians can be members of any nation judged by some to be less ...

" peoples who took over the territory of the

Western Roman Empire The Western Roman Empire comprised the western provinces of the Roman Empire at any time during which they were administered by a separate independent Imperial court; in particular, this term is used in historiography to describe the period fr ...

. They were especially used inlaid in gold cells in the cloisonné technique, a style often just called garnet cloisonné, found from

Anglo-Saxon The Anglo-Saxons were a Cultural identity, cultural group who inhabited England in the Early Middle Ages. They traced their origins to settlers who came to Britain from mainland Europe in the 5th century. However, the ethnogenesis of the Anglo- ...

England, as at

Sutton Hoo Sutton Hoo is the site of two early medieval cemeteries dating from the 6th to 7th centuries near the English town of Woodbridge. Archaeologists have been excavating the area since 1938, when a previously undisturbed ship burial containing a ...

, to the

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, ...

. Thousands of Tamraparniyan gold, silver and red garnet shipments were made in the

old world The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by th ...

, including to Rome, Greece, the Middle East,

Serica Serica (, grc, Σηρικά) was one of the easternmost countries of Asia known to the Ancient Greek and Roman geographers. It is generally taken as referring to North China during its Zhou, Qin, and Han dynasties, as it was reached via the ...

and Anglo Saxons; recent findings such as the Staffordshire Hoard and the pendant of the Winfarthing Woman skeleton of Norfolk confirm an established gem trade route with

South India South India, also known as Dakshina Bharata or Peninsular India, consists of the peninsular southern part of India. It encompasses the States and union territories of India, Indian states of Andhra Pradesh, Karnataka, Kerala, Tamil Nadu, and T ...

and Tamraparni (ancient

Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...

), known from antiquity for its production of gemstones. Pure crystals of garnet are still used as gemstones. The gemstone varieties occur in shades of green, red, yellow, and orange. In the US it is known as the

birthstone A birthstone is a gemstone that represents a person's period of birth that is usually the month or zodiac sign. Birthstones are often worn as jewelry or as a pendant necklace. History of birthstones Western custom The first century historian ...

for January. Gemological Institute of America, ''GIA Gem Reference Guide'' 1995, The garnet family is one of the most complex in the gem world. It is not a single species, but is composed of multiple species and varieties. It is the

state mineral Leaders of states in the U.S. which have significant mineral deposits often create a state mineral, rock, stone or gemstone to promote interest in their natural resources, history, tourism, etc. Not every state has an official state mineral, rock, ...

Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its cap ...

, New York's gemstone, and star garnet (garnet with

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visible wa ...

asterisms) is the state gemstone of

Idaho Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and W ...

Industrial uses

Garnet sand is a good

, and a common replacement for silica sand in sand blasting. Alluvial garnet grains which are rounder are more suitable for such blasting treatments. Mixed with very high pressure water, garnet is used to cut steel and other materials in water jets. For water jet cutting, garnet extracted from hard rock is suitable since it is more angular in form, therefore more efficient in cutting. Garnet paper is favored by cabinetmakers for finishing bare wood. Garnet sand is also used for water filtration media. As an abrasive, garnet can be broadly divided into two categories; blasting grade and water jet grade. The garnet, as it is mined and collected, is crushed to finer grains; all pieces which are larger than 60 mesh (250 micrometers) are normally used for sand blasting. The pieces between 60 mesh (250 micrometers) and 200 mesh (74 micrometers) are normally used for water jet cutting. The remaining garnet pieces that are finer than 200 mesh (74 micrometers) are used for glass polishing and lapping. Regardless of the application, the larger grain sizes are used for faster work and the smaller ones are used for finer finishes. There are different kinds of abrasive garnets which can be divided based on their origin. The largest source of abrasive garnet today is garnet-rich beach sand which is quite abundant on

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

n and Australian coasts and the main producers today are Australia and India. This material is particularly popular due to its consistent supplies, huge quantities and clean material. The common problems with this material are the presence of ilmenite and chloride compounds. Since the material has been naturally crushed and ground on the beaches for past centuries, the material is normally available in fine sizes only. Most of the garnet at the

Tuticorin Thoothukudi (formerly Tuticorin) is a port city, a municipal corporation and an industrial city in Thoothukudi district in the Indian state of Tamil Nadu. The city lies in the Coromandel Coast of Bay of Bengal. Thoothukudi is the capital a ...

beach in south India is 80 mesh, and ranges from 56 mesh to 100 mesh size. ''River garnet'' is particularly abundant in Australia. The river sand garnet occurs as a placer deposit. ''Rock garnet'' is perhaps the garnet type used for the longest period of time. This type of garnet is produced in America, China and western India. These crystals are crushed in mills and then purified by wind blowing, magnetic separation, sieving and, if required, washing. Being freshly crushed, this garnet has the sharpest edges and therefore performs far better than other kinds of garnet. Both the river and the beach garnet suffer from the tumbling effect of hundreds of thousands of years which rounds off the edges. Gore Mountain Garnet from

Warren County, New York Warren County is a county in the U.S. state of New York. As of the 2020 census, the population was 65,737. The county seat is Queensbury. The county is named in honor of General Joseph Warren, an American Revolutionary War hero of the Batt ...

, USA is a significant source of rock garnet for use as an industrial abrasive.

Cultural significance

Garnet is the

of January. It is also the birthstone of Aquarius and Capricorn in tropical astrology. In Persia this birth gem was considered a talisman from nature's forces like storm and lightning. It was widely accepted that garnet could signal approaching danger by turning pale.

United States

Garnet is

New York State's New York, officially the State of New York, is a state in the Northeastern United States. It is often called New York State to distinguish it from its largest city, New York City. With a total area of , New York is the 27th-largest U.S. state ...

official gemstone,

has

garnet as its state gemstone,

has star garnet as its state gemstone, and

Vermont Vermont () is a state in the northeast New England region of the United States. Vermont is bordered by the states of Massachusetts to the south, New Hampshire to the east, and New York to the west, and the Canadian province of Quebec to the ...

has grossular garnet as its state gemstone. Since 2003 New York State has ranked first in industrial garnet-production in the United States. Since there are just a few companies that account for all U.S. industrial garnet production, published detailed production statistics for New York State are not available. However, generally speaking, Barton Mines in Warren County is the largest U.S. garnet producer.

Collections

The New York State Museum in Albany, NY houses specimens from significant sites across the state, including 93 mineral species from the Balmat-Edwards mining district in St. Lawrence, super garnets from the Barton Mine in the Adirondack Mountains, and Herkimer diamonds from Herkimer County, New York

Oldest garnet mine

The largest garnet mine in the world is located Near North Creek New York and is operated by Barton Mines Corporation who supplies about 90% of the world's garnet. Barton Mines Corporation is the first and oldest industrial garnet mining operation in the world and the second oldest continuous mining operation in the United States under the same management and mining the same product throughout its history. The Gore Mountain Mine of the Barton Mines Corporation was first mined under the direction of H. H. Barton, Sr. in 1878 to produce garnet as the primary product.

Largest garnet crystal

The open-pit Barton Garnet Mine, located at Gore Mountain in the Adirondack Highlands, yields the world's largest single crystals of garnet; diameters range from 5 to 35 cm and commonly average 10–18 cm. Gore Mountain garnets are unique in many respects, and considerable effort has been made to determine the timing of garnet growth. The first dating was that of Basu et al. (1989), who used plagioclase-hornblende-garnet to produce a Sm/Nd isochron that yielded an age of 1059 ± 19 Ma. Mezger et al. (1992) conducted their own Sm/Nd investigation using hornblende and the drilled core of a 50 cm garnet to produce an isochron age of 1051 ± 4 Ma. Connelly (2006) utilized 7 different fractions of a Gore Mountain garnet to obtain a Lu-Hf isochron age of 1046.6 ± 6 Ma. We therefore conclude with confidence that the garnets formed at 1049 ± 5 Ma, the average of the three determinations. This is also the local age of peak metamorphism in the 1090–1040 Ma Ottawan phase of the Grenvillian orogeny and serves as a critical data point in ascertaining the evolution of the megacrystic garnet deposits.

References

External links

*http://www.gemstonemagnetism.com contains a comprehensive section about garnets and garnet magnetism.
USGS Garnet locations – USA
*http://gemstone.org/education/gem-by-gem/154-garnet *http://www.mindat.org/min-10272.html
Blog post on garnets
on the

Law Library of Congress The Law Library of Congress is the law library of the United States Congress. The Law Library of Congress holds the single most comprehensive and authoritative collection of domestic, foreign, and international legal materials in the world. Es ...

's blog *https://www.birthstone.guide/garnet-birthstone-meaning Garnet birthstone stories {{Authority control Magnesium minerals Symbols of Connecticut Symbols of Vermont Cubic minerals Minerals in space group 230 * * Industrial minerals